Increased blood viscosity in a patient with sickle cell anemia

Although intracellular viscosity is greatly increased in deoxygenated sickle cells, the viscosity of blood is not, because patients' packed cell volumes (PCV) are usually extremely low (15-25%). A young women with sickle cell anemia was admitted with a typical painful crisis, and was found to have a PCV of 39% with a reticulocyte count of 3.6%. During a hospitalization of 48 h, the PCV rose to 46%; her pain subsided but her behavior became bizarre, cardiopulmonary arrest occurred, and she could not be resuscitated. At autopsy, no abnormalities were found except for congested blood vessels containing sickle cells. It was subsequently discovered that she and her family had been exposed to carbon monoxide for a week prior to admission. Blood samples from another patient studied with a PCV of 40% showed progressively decreased viscosity if they contained 13-20% carboxyhemoglobin. It is suggested that preexisting accelerated erythropoesis was further stimulated by CO, and caused "compensatory polycythemia", but that the CO prevented most of the newly formed cells from sickling and being destroyed. Admission to hospital caused a gradual disappearance of CO but the patient's PXV continued to rise. Her death may have been due to a rare form of hyperviscosity syndrome, when the level of carboxyhemoglobin in her blood fell to more normal levels and her cells regained the ability to sickle. Treatment of sickle cell anemia with an effective non-covalently bound agent could have a similar effect, if the agent were withdrawn abruptly.